A police officer told a jury at Exeter crown court how she arrested two men accused of plotting to kill the soul singer Joss Stone after local people raised the alarm in June 2011.

PC Victoria Dixon said she was the first officer to arrive at the scene in the Devon town of Cullompton, where she found a samurai sword in the boot of the men's battered Fiat Punto, along with two hammers, a metal spike, gaffer tape and black bags.

She also recovered a printout of a map of Devon, where the singer lives, that included the words: "Here Joss Stone."

The jury was shown the sword and other items.

When Dixon asked the men what they were doing, one – Junior Bradshaw – said they had got lost while visiting a friend and were trying to find their way back to the motorway.

The prosecution alleges that Bradshaw, 32, and Kevin Liverpool, 35, conspired to rob and murder the 25-year-old singer. The men deny both charges and an allegation of conspiring to cause Stone grievous bodily harm.

Notes found by the police allegedly suggest the two, who lived together in Manchester, planned to decapitate Stone – whom they called a "she-devil" – and throw her body in a river.

The prosecution has said their motive could have been financial but another note hinted they might have had a grudge against Stone because she had sung for the royal family and had been invited to Prince William's wedding.

The jury also heard from psychiatric nurse Albert Hoogland, who said Bradshaw had been released from Manchester Royal Infirmary 14 months before the alleged plot.

He said care workers thought it was not appropriate for him to move in with Liverpool – whom he referred to as his "cousin" though they are not related.

Hoogland said Bradshaw may have stopped taking his anti-psychotic medication but he saw him while he was living at the flat and did not consider his condition to have relapsed.